1. Technical Field
The present invention relates to an organic electroluminescent (EL) display device and a method for producing the same.
2. Description of the Related Art
There have been recent advancements in the development of organic electroluminescent (EL) display devices as thin type display devices.
FIG. 9 schematically shows one example of the constitution of a display panel of an organic EL display device. In an organic EL display panel 30, an organic EL element is formed on a substrate 31, and the EL element includes an anode (lower electrode) 32, a hole transportation layer 33, a light emitting layer 34, an electron transportation layer 35, a cathode (upper electrode) 36, and a protective layer (sealing member) 37 is also provided in order to prevent degradation of the organic EL element due to oxygen, moisture and the like.
When producing an organic EL display device provided with the organic EL display panel 30 having the above-described structure, the following steps may be carried out.
On a substrate 31 made of a transparent material such as glass, a transparent anode (extraction electrode) 32 made of ITO or the like is formed through vacuum deposition, and, subsequently, an insulating layer and barrier wall (not shown) are formed. Then, by using a shadow mask, the hole transportation layer 33, the light emitting layer 34, the electron transportation layer 35 and the like are sequentially formed in a predetermined position through vacuum deposition (mask deposition), followed by film formation of the cathode 36 made from Al, MgAg or the like. Incidentally, the organic EL layer 38 is not limited to the configuration shown in FIG. 9, but may have various configurations, including, for example, a configuration having no transportation layers 33 and 35, or having an injection layer between electrodes 32 and 36 and transportation layers 33 and 35, or having a so-called multiphoton emission element in which light emitting layers and the like are laminated in series.
By selectively applying a voltage between the lower electrode (anode) 32 and the upper electrode (cathode) 36, the light emitting layer 34 emits light, and the light from the light emitting layer 34 is made to leave the transparent substrate 31 via the anode 32. Display panels in which the light from the light emitting layer 34 is made to leave from the transparent substrate 31 side in this way are referred to as “bottom emission” panels.
Contrastingly, organic EL display panels having a so-called “top-emission” structure, in which a transparent electrode is used as an upper electrode and the light is made to leave from the upper electrode side, have been also developed.
In transparent organic EL display panels, and organic EL display panels having a top-emission structure or the like, when a transparent electrode material such as ITO or the like is used for an upper electrode or upper electrode wiring, since such a transparent electrode material has a high resistivity, the voltage at the cathode wiring portion decreases by a large amount, and the element cannot be supplied with sufficient voltage, and as a consequence the brightness of the panel decreases. Known methods for overcoming this problem include methods such as forming an auxiliary electrode to be connected to the upper electrode (for example, see Japanese Patent Application Laid-Open (JP-A) Nos. 2005-203196, 2005-235491, and 2005-267991).
FIG. 10 shows one example of the configuration of an organic EL display panel of the related art that is provided with an auxiliary electrode, and FIG. 11 schematically shows the A-A′ cross-section of an organic EL display panel 70. In FIGS. 10 and 11, components with the same symbols indicate the same components. In the organic EL display panel 70, after sequentially forming a lower electrode 72 and an insulating layer 77 on a substrate 71, an auxiliary electrode 74 for the upper electrode is formed so as to protrude toward the inside of an emitting region at one corner thereof. Then, an insulating barrier wall 76, an organic EL layer 73, and an upper electrode 75 are formed sequentially, wherein the portion 74a of the auxiliary electrode 74 which protrudes toward the inside of the emitting region, and the upper electrode 75 are connected to each other (see JP-A No. 2004-103582).
However, there are problems when using a structure wherein a part of an auxiliary electrode is formed so as to protrude towards the inside of the emitting region as described above; namely, for example, the openings become narrower, the effective pixel regions become smaller, and more complex production processes are required.